High-frequency signaling



B. W.'KEND ALL. HIGH FREQUENCY SIGNALING,

APPLICATION FIEED NOV. 29,1915.

' Patented Feb. 10,1920.

'Affy.

UNITED STATES PATENT OFFICE.

-.BURTON w. KENDALL, on NEW COMPANY, mconromrnn, 30m

YQRK, N. Y., 'ASSIGNOR WESTERN ELECTRIC OF NEW YORK, N. Y.,

A CORPORATION OF NEW HIGH-FREQUENCY SIGNALING.

Specification of Letters Patent. Patented Feb. 10, 1920.

Application filed November 29, 1915. Serial No. 64,005.

To all whom it may concern:

Be it known that I, BURTON W. K NDAL a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented-certain new and useful Improvements in High- Frequency Signaling, of which the follow-. ing is a full, clear, concise, and exact description.

This invention relates to a method and cation, with small regard for the distortion produced.

. .the difference In the case of wireless telephony, however, where the high frequency carrier waves are modulated in accordance with the speech signals to be sent, the problem -is much more difiicult, for the intelligibility of the translated signals depends on the faithful reproduction of the modulations of the carrier waves. This means tion must be kept to a minimum.

The method .of intensification which is here shown depends upon the local generation of oscillations at the receiving station, which oscillations are combined with the received oscillations to produce a much stronger effect in the indicator than would be produced by the received oscillations alone. a

A method of wireless telegraph reception, which hasnow becomewell known in-the art, i the heterodyn'e method, which consists essentially in receiving the weak signal oscillations and combining them generated oscillations ofa slightly different frequency. This results in the production of beats which are of a frequency equal to between the frequency ofthe received and oscillations. Thi difference is adjusted to be within the audible limit, and a note corresponding to this beat frequency is heard in the receiver. However, the pitch of this note depends in no way on the form of the transmitted wave. but only on the difference in frequency between the transn'ntted high the extraordinary that the distorany desired frequency, preferably with locally I that of the locally generated 'a plate 32, all suitably evacuated vessel 33. The input cirfrequency oscillations and the locally generated oscillations.

While-this method is well adapted for telegraphic messages-, it cannot, of course, be used for-telephonic signaling. It has been found, however that by generating local oscillations of a frequency identical to the carrier frequency and combining them with the received high frequency oscillations, one can receive oscillations which have been modulated in accordance with speech, and that the resulting translated signals in the 1eceiver are highly intensified. It is obvious that .the resulting translated signal in the receiver will also be intensified in case the modulation is not inaccordance with speech but in accordance with a musical note, for instance. The invention is of particular advantage'in any case where a faithful reproduction of the signal is desired.

The inven ion will be better undetstood by v reference to the following specification and accompanying drawings, in which Figure l shows a receiving station embodying this invention; F ig. 2 shows a modification in which'the receiving circuit itself generates the local oscillations; Fig. in which-the received oscillations are first amplified and then combined with local oscillations of carrier frequency; is a modification of Fig. 3.

Referring to the drawings, in each of the figures 10 representsa receiving antenna of the usual type employed, in wireless signaling. This antenna is connected to ground at 11, and between the antenna and the ground connection are placed ductance 12 and condenser 13, by means of which the receiving system may be tuned to a suitable variable 1n-' the fre- 3 shows a circuit and Fig. 4 v

quency-Iof the signal which are to be rece ved. This condenser may a very high non-inductive resistance or may be omitted entirely.

shown .in Fig. 1 is a tuned circuit consisting of theinductance 20 and the condenser 21. Connected in shunt to the condenser21 is a detector, and there is, in this case, shown a detector of the audion type which comprises the usnalheated filament 30, a grid 31 and these being contained in a cuit of this detector comprises the filament 30 and the grid 31, and these are connected in shunt, as mentioned above, to the conbe shunted v Inductively associated with the antenna denser 21. The output circuit includes the filament 30 and the plate 32 and contains in series a suitable source of electrical energy 35, and a telephone receiver 36. In the in put circuit of said detector it is desirable to insert a battery 37 in such a manner that a negative pole shall be connected to the grid. A condenser 39 is placed in shunt to the receiver36 in order to We a low impedance .path to such high frequency oscillations as pass through the output circuit.

As thus far described, this system is adapted to receive modulated oscillations and to translate them into audible signals in the receiver 36. The intensity of these.

receiver 36. In fact, it can be shown that, w1 th1n certain limits, if B is the amplitude of the received modulated wave and A is the constant amplitude of the locally generated .oscillations impressed upon the receiving circuit, the intensity of the signals received at 36 will be approximately proportional to the product of A and Br While in this figure there is shown and described a detector of the audion type, it is to be understood that any other detector,

. such as acrystal rectifier, may be used although a detector of the form shown is pre ferred. Also, it is to be understood that While the locally generated oscillations may be set up by an independent generatorof any type, such as shown at '40, one may make use of that property of famplifiers and repeaters by virtue of which they mayv act as generators of oscillations in themselves. Such a-circuitis shown in-Fig. 2, in which a coupling between the input circuit and the output circuit of this thermionic device is obtained by connecting the filament to some intermediate point 50 of the inductance 20. In this case, as is described in application of Hartley, Serial No. 31,47 6, filed June 1, 1915, local oscillations will be set up in this receiving circuit, the intensity and frequency of which will be determined by the point of contact 50andby the period of -feed-back circuit 67 connected in series in the circuit as determined by 20 and 21. In this case also, it hasbeen found convenient to insert a variable non-inductive resistance 51, which assists materially in determining the intensity of the locally generated oscillations as shown in application. of Heising, Serial No. 51,761,'fi1ed September 21, 1915.

A circuit arranged amplifying circuit comprising the tuned "circuit 60, 61', connected to the input circuit of a thermionic amplifier of the audion type, this input circuit including the usual heated filament 62 and grid 63, and the out- 5 put circuit including the filament 62 and the plate 64; in series with a power "battery 65 and an inductance 66. The usual battery 68 for polarizing the grid may also be used. Inductively connected to the inductance 66 1s a detecting circuit, such as circuit D of Fig. 3.- This circuit D has a circuit 20, 21 tuned to the carrier frequency and inductively coupled to inductance 66. In shunt to the condenser 21 isadetecting and generating thermionic device 33, similar in every respect to the one described in Fig.

2. The outputcircuit of this thermionic device 33 contains the power battery 35 and 1 the telephone receiver 36, said receiver being shunted by the condenser 39. In series with this output circuit is also included the inductance 70 which is coupled to the coil 20, thereby arranging for the feed-back of power from the output to the input circuit,

causing the circuit as a Whole to generate oscillations in a'manner similar to that described in connection with Fig. 2. It is to be noted that this coil 7 0 should'be so arranged with respect to 20 that singing or generating shallf be produced. -While- I describe and show this specific circuit D for generating local oscillations, it is to be pointed 'out that ,any suitable source of oscillations may be used, and in place of this circuit D, we may use the circuit B of Fig.2 or the circuit of Fig. 1. In this latter case, it is, of course,

obvious that a separate source of oscilla-- tions, such as 40, 41 of Fig. 1, will be required. 1 1

It is a known fact that, in view of the inherent-electrostatic coupling between the input and the output/circuits of an amplifier, as broughtabout by the elements in the vacuum tube, and in View of the electrostatic and electromagnetic coupling unavoidable in the circuit connections, there is a tendency for such an amplifier to sing, and it'has been found, in the case of the amplifying circuit C, that it is' desirable to prevent such singing', and for this purpose.one may supplya In Fig. 4 there is shown an amplifying output circuit for the detector. As shown in.

said figure, there is placed in series with the power battery sistance 8O. Parallel to this output circuit is a circuit containing the relatively large condenser 81 and the primary 82- of a low frequency transformer 82, 83. In shunt to the primary 82 is a circuit containing the inductance and the condenser 73. The coil 70 acts to feed back high frequency power from the output to the input circuit of the vacuum tube. The condenser 7 3, which is of relatively low capacity, is used to prevent the short circuiting of low frequency oscillations through the coil 70. In this arrangement, the high frequency output of the vacuum tube passes through the circuit 70, 73, and the low frequency oscillations pass through the coil 82 while the direct current passes through the resistance 80.

In series with the coil- 83 is the non-inductive resistance 84. In shunt to a part of the resistance 8% is the input circuit of a thermionic amplifier 85 comprising the usual heated filament 86 and grid 87. The output circuit comprises the filament 86 andv the plate 88, as well as the power battery 89 and the primary 90 of a transformer 91. This transformer is a telephone repeating coil. The secondary of this repeating coil is connected to the telephone receiver 92 or to any telephone line for further transmission to remotestations. It may be advantageous to place the polarizing battery 98 in the grid circuit of the amplifier to maintain the grid at a proper potential with respect to the filament. In practice, it is desirable that the transformer 82, 83 shall be adapted to work between circuits of high impedance, and that the resistances 80 and 8f shall be large. \Vith the thermionic detectors which I have commonly used,I find that the resistances 80 and 84 may be of the order of one hundred thousand ohms. In this last figure, it will be noted that the circuit E is used solely for amplifying the received hi h frequency oscillations, while the circuit F is used for combining these amplified oscillations with locally generated oscillations of the carrier frequency. and thatthe combination gives low frequency oscillations varying in accordance with the signal which was transmitted, and that these rectified or translated signals of audio=freouency are then amplified in the circuit G previously to being received in the telephone receiver 92. It will be noted that the feed-back coil 67 isso connected with respect to the coil 60 as to prevent sinnin in the same manner as for this coil 67 in Fig. 3.

In this 35 a high non-inductive re-' ing system,

.quency, a

de cribed While this invention has been described in connection with'a wireless telephone. system, it will be obvious to one skilled in the art that the invention is not limited in all 're spects to such systems, but that in certain aspects it is equally well adapted to wire systems in which modulated high'frequency signals are se'nt'outfrom one station and received- -at another.

What is claimed is:

1 The method of wireless telephony which consists in radiating high frequency carrier oscillations modulated in accordance with speech, in receiving said oscillations, in generating local oscillations of said carrier frequency and combining them with the received oscillations.

2. Tl-16 method of" wireless telephony' which consists in radiating modulated high frequency oscillations, in receiving said oscillations and combining them with locally generated high frequency oscillationsof the same frequency as and of constant amplitude.

3. The method of high frequency signal:

' transmitting high fre ing which consists in quency carrier waves modulated in accordthe received oscillations ance with speech, receiving said modulated 7 high frequency waves, generating at the receiver. oscillations of the carrier frequency,

combining said locally generated oscillations with the received oscillations, impressing said combination on a detecting device, and translating the resultant combination into audible signals in accordance with the transmitted signals.

4. The method of signaling, which consists in transmitting modulated carrier, oscillations, in receiving said oscillations, amplifying said oscillations, generating oscil ceiving station, and in combining the amplified and locally generated oscillations to reproduce the signal. i I 5. In a high frequency telephone receiva receiving conductor adapted to receive high frequency carrier oscill'a tions modulatedin accordance with speech,

a generator'of oscillationsof the carrier frea generator of oscillations of the carrier fredetector, a circuit to'impress the received oscillations and the locally gen-. euated oscillations upon the inputcircuit of tlie detector, and a translating device associated with the output circuit of the detector.

I lations of the carrier frequency at the refrequency carrier oscillae I tions modulated n accordance with speech,

7. In a high frequency telephone receiving system, a receiving conductor'adapted to receive high frequency'carrier oscillations modulated in accordance with speech, a gem 5 jerator of oscillations of the carrier fre-, quency, a detector, a-circuit tuned to carrier frequency to impress the received. osci1lations and the locally generated oscillations upomthe input circuit of the detector, and atelephone receiver associated with the output circuit of the detector.

' 8. A high frequency telephone receiving system comprising an antenna adapted to receive high frequency'carrler Waves modulated in accordance with speech, a detector,"

atuned circuit connected to said antenna and to theinput circuit of said detector, a generator of oscillations of the carrier frequency, means-for impressing said locally generated oscillations upon said input circuit simultaneously with the reception of the speech modulated oscillations. v

-9. A high frequency telephone receiving system comprising an antenna adapted to receive high frequency carrier Waves modulated in-accordance With speech, a thermionic detector of the audion type, a tuned circuit inductively connected to said antenna and connectedto the input circuit of said detector, a generator of oscillations of the car-v rier frequency, means forimpressing said locally generated oscillations upon the, input modulated in accordance with speech, and

a telephene receiver associated with the output circuit of said detector.

11.' In a wireless telephone receiver 'sys' M tem, a thermionic device of t e audion type,

means for impressing up the input circuit of said thermionic devic received high. frequency carrieroscillations modulated in accordance with speech, means for causing saidtherm-ionic device to generate osci-lla-' tioiis of'the carrier frequency and for impressing said locally generated oscillations ;upon the input circuit of said thermionic device simultaneously with the receipt of the modulated high frequencyoscillations, and

a telephone-receiver associated .withthe output circuit of said thermionic device.

12. A system for detecting modulated carrier oscillations, said system comprising an electric discharge device having an an: 'ode,'a cathode, and anjmipedance-controloscillations; P

ling eleinent,--an input circuit and an output circuit, means for causing said output circuit 'to react upon said input circuit to set up oscillations, and means causing the fre quency of theoscillationsthus set up-ttbe the same as that ofvthe modulated carrier -13.- A signal receiving system comprising an electr1c discharge device having a cathode, an anode, an impedance-varying elemerit, an input circuit and an output circuit,

means for impressing upon said input circuit carrier oscillations modulated in accordance with variable low frequency waves, means for causing said discharge device to generate oscillations of the carrier frequency and for impressing said locally generated oscillations upon said discharge device simultaneously with said modulated oscillations,

and signal-reproducing with said output circuit.

14. A receiving system comprising .a detector, means for impressing upon the input circuit of said detector carrier oscillations means associated modulated in accordance with a relatively low frequency wave, a local generator of oscillations of-the carrier frequency, means for" impressing upon said detector the locally-generated oscillations and the modulated oscillations, and a translating device associated with the output circuit of said detector for receiving and utilizing the detected oscillation-s.

15. A receiving system comprising'means .for amplifying weak oscillations, means for impressing the-received oscillations modulated in accordance with a low frequency wave upon said amplifying means, a local generator of oscillations of the frequency ofsaid modulated oscillations, translating means for obtaining low frequency waves from oscillations modulated in accordance with waves of said low frequency, and means for impressing said received modulated oscillations and said locally-generated oscillation-s simultaneously -upon said translating means.

16. A telephone receiving system comprising means for amplifying weak oscillations, means for impressing received oscillations modulated in accordance with speech upon said amplifying means, a local generator of oscillations of the frequency of" said received oscillations, translating means for obtainng low frequency waves from oscillations modulated in accordance with waves" of said low frequency, and means for impressing said received oscillations and said) locallyrgenerated oscillations simultaneously upon said translating means.

In witness whereof, I hereunto subscribe BURTON W. KENDALL-.1-

my name this 26th day (if November A. D., I 1915. a 

